Imaging on Film RVT: Chapter 5

Learning Objectives: Chapter 5 Identify cassettes, screens, and film, and understand how they work together to create an image Understand latent image formation Understand correct storage and care of film and cassettes

The Image Receptor Device that receives the x-rays and produces an image Receptor components in film-based imaging: Cassette Intensifying Screen Film

The X-Ray Cassette Hard, outer casing for a pair of intensifying screens and one sheet of film. Must have the following properties: Sturdy and unbendable Protects the two other parts from damage Must support the weight of your patient Must latch closed securely Film must not be exposed to light Washable outer layer Cleaning solutions, blood, fur, etc. Radiolucent - permitting the passage of radiant energy, such as x-rays, with little attenuation, the representative areas appearing dark on the exposed film. Radiopaque - Not allowing the passage of x-rays or other radiation Different forms today include aluminum, polycarbonate, magnesium, and carbon fiber.

The X-Ray Cassette More properties: Radiolucent front “Front” is placed nearest the patient Lead lined back (facing away from the patient) Absorbs scatter radiation

Inside The Cassette Both sides lined with felt or foam pressure pads to ensure close contact of the film to the intensifying screens Referred to as Film/Screen contact Some companies also arch the back of the cassette to create even better contact If inadequate, image appears fuzzy

Poor Film/Screen Contact

Film Cassette

The Cassette Sizes vary Correspond to screen and film sizes. Cost varies as well. *Film is sold in specific sizes to match the cassette size

Lead Blocker Found in corner of cassette Prevents irradiation of the part of the film necessary for identification. Be careful not to have any important body part obscured

Cassette Maintenance Handle with care Cassettes should be kept clean Common damage includes: dropping, bodily fluids Cassettes should be kept clean Use mild soap and water on a regular basis Cassette storage: Upright and away from radiation Do not stack Should always be loaded and ready to use Avoid humidity & dust Tip: Number the cassettes so repeat problems can be easily identified

Intensifying Screens Made of three layers: Fluorescent sheets of plastic that convert x-ray radiation into visible light. Found in between the cassette and the film Made of three layers: Base- plastic polymer that is very sturdy Adhesive layer- holds emulsion layer onto base Emulsion layer- contains phosphor crystals Phosphors are what convert x-radiation to light This is called ____________________.

Intensifying Screen: Emulsion Layer Phosphors are elements that are efficient at capturing photons. The intensity and color of this light are determined by the choice of phosphor Calcium tungstate was original choice Emit a blue light ______ _________ phosphors have been found to be much more efficient Emit green light Ex. Lanthinum oxybromide phosphor Phosphor also determines the _________ at which the x-rays are converted to light

Intensifying Screen: Speed Screens are rated by their speed Rare earth phosphors convert much quicker than tungstate This means less exposure time required! Thick emulsion layers convert much quicker than thin emulsion layers Fast screens reduce radiation exposure, but lose quality detail Many manufactures, different screen ratings Both types still available today

Intensifying Screens Why do we need these screens? Film is more sensitive to light than to x-rays Only _______ of exposure results from ionization of x-rays. Where does the rest come from? Screens reduce the amount of radiation required to produce a diagnostic radiograph What factor determines the amount of x-rays produced? What factor determines how long they are produced for?

Intensifying Screens: Safety First! If we can decrease mAs … Decreases radiation dose to patient/operator Reduces the chance of motion on the radiograph

Intensifying Screens 2. Enhances contrast Contrast between different parts of anatomy is required for an x-ray to be diagnostic Large amount of x-rays produce more secondary and scatter radiation leading to ______ _____________ on the film.

Intensifying Screen: Color Blue-emitting screens Film must be made to react to blue light This system is being phased out Green-emitting screens Kodak introduced in the 1980’s Superior system Must be aware of which screen is being used in order to match the film color! *Note: green film can see both blue and green light

Intensifying Screen: Care Ensure screen integrity is maintained during unloading of film Let the film fall away naturally Screen cleaners Manufactured cleaners should be used annually Always rinse with distilled water to remove any residue Screens should be checked for scratches, bends and wear regularly Can replace if needed

X-ray Film Strong, yet flexible translucent material, made of a light & x-ray sensitive emulsion, coated in a protective gelatin. Design: Screen – Sensitive to wavelengths emitted from intensifying screens Requires less exposure Non-screen – Designed for direct exposure Needs extra-long exposure times

X-ray Film: Layers Film Base – bend w/o stretching; withstand changes in temp and humidity; polyester Film Emulsion – Contains the photosensitive silver- based products, suspended in a gelatin layer Produces the image Super coat – Tough, protective coating of hard gelatin

X-ray Film: Emulsion Gelatin provides support for photosensitive crystals Provides an even suspension throughout Contains mainly silver __________ crystals Also silver iodide and silver chloride This composition is termed silver halide Double emulsion: emulsion layer on each side of the base Quicker to react to light, less radiation required

Latent Image Formation Latent- it’s there, but hasn’t been developed yet Image formation begins when x-rays and light activate the silver crystals. X-rays are sent from the __________. Light is produced by the ___________ ______. Silver halide particles move toward sensitivity specks to form the lattice network Happens by electromagnetism

X-ray Film: Sensitivity Specks Imperfections within the silver halide crystals Requires aging (time in the warehouse) Ratio of 3 Ag:1 speck required *Without these, the silver would not “move” to form the lattice network

X-ray Film: Lattice Network The arrangement of silver and sensitivity specks, that when developed will form the anatomical image Easily disrupted Pressure before exposure from improper __________. After exposure from _________________ the cassette. Leads to artifacts on film Streaks will radiate from point of impact Breaks down over time

Film responds to light emitted from the screens X-ray film: Color Film responds to light emitted from the screens Blue-receiving film appears physically green Green-receiving film appears violet To have a visible identifier Due to the antihalation dye *Added to prevent reflection from one intensifying screen onto the opposite emulsion layer

X-ray Film: Storage Unopened film boxes should be stored on edge Film is pressure sensitive Open boxes must be stored in a light-tight designated film box Must be protected from radiation Must be protected from light Film darkening: Due to heat and aging Check expiration dates!